I need to check if a uploaded file in a grid have a valid digital signature.
Can this be done before the form is submited ? In case of invalid digital signature, the user has a alert to replace the invalid files.
Thanks

If you don't want to use those two methods, you can upload an image file that contains a digital signature. I don't know of any way to check it, aside from verifying that it is an image file. If that is all you want, then these code examples will help you get started:https://www.pmusers.com/index.php/Multiple_Files